Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08G—TRAFFIC CONTROL SYSTEMS
  • G08G5/00—Traffic control systems for aircraft, e.g. air-traffic control [ATC]
  • G08G5/0017—Arrangements for implementing traffic-related aircraft activities, e.g. arrangements for generating, displaying, acquiring or managing traffic information
  • G08G5/0026—Arrangements for implementing traffic-related aircraft activities, e.g. arrangements for generating, displaying, acquiring or managing traffic information located on the ground
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C23/00—Combined instruments indicating more than one navigational value, e.g. for aircraft; Combined measuring devices for measuring two or more variables of movement, e.g. distance, speed or acceleration
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
  • G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
  • G01S1/04—Details
  • G01S1/047—Displays or indicators
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
  • G01S19/07—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing data for correcting measured positioning data, e.g. DGPS [differential GPS] or ionosphere corrections
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/13—Receivers
  • G01S19/14—Receivers specially adapted for specific applications
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/13—Receivers
  • G01S19/14—Receivers specially adapted for specific applications
  • G01S19/15—Aircraft landing systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/0009—Transmission of position information to remote stations
• • G—PHYSICS
  • G08—SIGNALLING
  • G08G—TRAFFIC CONTROL SYSTEMS
  • G08G5/00—Traffic control systems for aircraft, e.g. air-traffic control [ATC]
  • G08G5/0004—Transmission of traffic-related information to or from an aircraft
  • G08G5/0013—Transmission of traffic-related information to or from an aircraft with a ground station
• • G—PHYSICS
  • G08—SIGNALLING
  • G08G—TRAFFIC CONTROL SYSTEMS
  • G08G5/00—Traffic control systems for aircraft, e.g. air-traffic control [ATC]
  • G08G5/0073—Surveillance aids
  • G08G5/0082—Surveillance aids for monitoring traffic from a ground station
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
  • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
  • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
  • G01S19/53—Determining attitude

Definitions

• the present airport control systems rely heavily on a radar display screen that shows the location of aircraft in flight in a two dimensional format; the individual planes are labelled for altitude and other factors; unfortunately, much of the work involves visual observation through the control tower window and verbal communication.
• No. 4,890,232 for instance, has to do with a visual display apparatus for showing the relationship of two separate aircraft on converging runways.
• the patent of GERSTENFELD, No. 4,827,418, describes an expert system for training control operators.
• the patent of GRAHAM et al. , No. 4,811,230 shows a flight management computer that includes an intervention system.
• the patent of THURMAN, No. 4,706,198, describes a computerized airspace control system invoking a master control system and regional control units.
• a patent to SCHWAB et al., No 4,516,125 shows apparatus for monitoring vehicle ground movement in the vicinity of an airport and involves the processing of radar return video signals.
• Another object of this invention is the provision of a control/management system, especially for aircraft control, in which a 3-dimensional display is produced to show the information necessary to operate an airport.
• a further object of the present invention is the provision of a means for handling increased traffic at an airport without loss of safety.
• a still further object of the invention is the provision of a system for superimposing a 3-dimensional display of local aircraft paths on an accurately-configured map of the local space.
• Another object of the invention is the provision of an improved surveillance system for airport arrival and departure aircraft separation.
• Another object of the invention is the provision of an airport control/management system that is suitable to the task of providing for increased traffic, while maintaining safety; that will enjoy a wide and growing market acceptance with declining life cycle costs; and that will integrate easily with other parts of the air traffic control and aircraft navigation systems.
• the present invention has to do with an airport control/management system which has a means for establishing a precise 3-dimensional digital map of a selected airport space envelope, the map containing global positioning system reference points.
• a computer with a monitor screen is provided for receiving and displaying the 3-dimensional map.
• Means is provided that is located on at least one vehicle in the airport space envelope to receive continuous global navigation satellite system (GNSS) signals, calculate position, velocity, heading, and time and transmitting the information to a receiver associated with the computer.
• Means is provided within the computer to display a 3-dimensional image corresponding to the vehicle path on the 3-dimensional map.
• GNSS global navigation satellite system
• the global navigational satellite system includes a constellation of space satellites and the computer contains a program for manipulating the image of the vehicle path and the map together to a desired apparent line of observation.
• Figure 1 is a generally schematic view of an airport control/management system incorporating the principles of the present invention.
• Figure 2 is a plan view of an airport with a vehicle path imposed, as it appears on a computer screen in the system,
• Figure 3 is a view of the airport and vehicle path as it appears on the screen with a 20-degree viewing angle
• Figure 4 is a diagram showing the pattern generated by the vehicle in take-off mode
• FIG. 5 shows a block diagram of a radio-based data link system which embodies the principles of the present invention
• Figure 6 is a plan view of an airport with a trajectory path, waypoints and onumented survey points imposed, as it appears on a computer screen in the system.
• Figure 7 describes the airport terminal system hardware components which embodies the hardware principles of the present invention.
• Figure 8 describes the airport terminal system software components which embodies the software principles of the present invention
• Figure 9 describes the aircraft/vehicle system's hardware components which embodies the hardware principles of the present invention.
• Figure 10 describes the aircraft/vehicle system's software components which embodies the software principles of the present invention
• Figure 11 shows aircraft in 3-D airport map.
• Aircraft are 3-D scaled representations of real aircraft. Aircraft are drawn into the map from a data base of various aircraft types.
• the airport control/management system is shown as including a map generator 11 for establishing a precise 3-dimensional digital map of a selected airport space envelope.
• the map contains global positioning system reference points.
• the system includes a computer 12 having a monitor 13 with a screen 14. The computer and screen serve to receive and display the 3- dimensional map.
• a GNSS receiver 15 is located in a vehicle 16 (#1), which is located in the airport space envelope.
• the GNSS receiver calculates the position, velocity, time and heading, possibly using reference station corrections. These signals are transmitted to a receiver 17 which, in turn, is connected to the computer 12.
• the computer contains a program to use the said signals to superimpose a 3-dimensional image corresponding to the vehicle path onto the 3-dimensional map.
• the GNSS receiver incorporated in the vehicles contains, in the usual way, access to space satellites 18.
• the computer 12 contains a computer-aided-drawing (CAD) program 24 that is capable of manipulating the image of the vehicle path and the map to a desired apparent point of observation.
• a secondary screen 19 may be provided at a suitable airline facility, to show the location and movement of the airline's own vehicle (#3, for instance).
• Figure 2 shows the image 21 as it appears on the monitor screen 14 when the 3-dimensional map 22 of the airport (generated by the generator 11) has the path 23 of a vehicle, such as vehicle #1, imposed upon it.
• This is a plan view in which the airport map is shown as it appears from directly above and as the vehicle path appears from the same vantage point.
• the term ⁇ airport can, of course, include not only conventional land-based airports, but also vertiports, heliports, and sea bases.
• Figure 3 shows the appearance of the screen 14 when the computer aided drawing program 24 is used to rotate the image to an aspect which is 20 degrees out of the horizontal.
• the vehicle is shown in the taxi to take-off mode, but, of course, the appearance would be somewhat similar if it were in the landing mode.
• the operation and advantages of the invention will now be readily understood in view of the above description.
• the method of establishment of a precise 3-dimensional digital map 22 is well-known and makes use of photogrammetry and stereoscopic digitalization techniques.
• the digital information contained in the map generator 11 is then applied through the computer 12 to the screen 14.
• the map 22 appears on the screen and the resulting image can be manipulated by use of the computer- aided drawing program 24 to show the appearance of the airport space envelope as it appears from any desired angle and at any distance.
• This manipulation is controlled by means of a keyboard 20, other standard input device, such as a mouse or tablet, or resident applications software.
• the next step consists of receiving GNSS signals, using an antenna designed for this purpose.
• the on-board receiver on the aircraft 16 performs the necessary calculations and then transmits the results using a transmitter 15 within the vehicle.
• the equipment makes use of satellites 18 whose position relative to the earth's center of mass is precisely known.
• the transmitter 15 sends information as to the aircraft's location, speed, heading, identification and time of transmission to the receiver 17 and this is presented to the computer 12 for display on the screen 14.
• the information thus transmitted generates an image 21 on the screen which represents a three-dimensional picture of the vehicle path 23 superimposed on the map 22.
• the image 21 thus produced can be rotated by the CAD program 24 to any desired angle and zoomed to enlarge or decrease the size.
• Figure 2 shows the appearance of the image 21 in plan, i.e., as the airport and aircraft path appear when viewed from directly above.
• Figure 3 shows the image when the observation angle is 20 degrees above the horizontal. It can be seen, then, that an accurate visualization of the vehicle's progress is made possible by selecting various angles of view, as desired.
• the chart of Figure 4 shows a typical elevation profile of an aircraft as it moves about the airport preparatory to taking off and then as it takes off.
• the image 21 can, of course, be transmitted and displayed on other screens; for instance, the screen 19 is located in the facilities of an airline whose vehicle #3 is within the airport space envelope.
• the screen image may show only that vehicle, or, if desired, may show the same complete image (with other vehicles that is shown on the main screen 14).
• the image 21 can also be displayed on a screen in the aircraft or other airport vehicle. Again, the screen image may show only that vehicle or, if desired, the same or another image that is shown on the main screen 14.
• the present inventive system provides an integrated airport planning and design tool. It incorporates available technologies of the type that will play an important future role in aviation
• Air transportation is expected to grow at a large rate in the next few years. The predicted growth will place a substantial load on existing airports. Present airports will need to be modernized to support such growth.
• the present invention serves to satisfy three primary objectives.
• the three objectives are: (a) suitability for the task, (b) a wide market acceptance with 20 declining life cycle costs, and (c) ability to integrate easily with other parts of the air traffic control and aircraft navigation systems.
• the computer used was a personal computer with 3-D graphics.
• the global position system was the NAVSTAR GPS utilizing earth centered, earth fix (ECEF) coordinates and using the ECEF world geological survey (WGS-84) which was ellipsoid-adjusted for geoid
• the separation was -28.3 meters mean sea level (MSL) elevation at Manchester,- N.H. and used in the 3-D map converted between latitude/longitude and N.H. state plane and other coordinates.
• the computer used the MSDOS operating system or SCO XENIX OS operating system with modem capability.
• Each layer could be specified for particular function such as air traffic control, airline or airport operations.
• the system operator could select one or more layers to be displayed. In this way, only information relevant to his present function would be displayed.
• Another feature of the system involves the use of precise multi-monumented survey points in airport area for local coordinate conversions and real time map displays.
• forbidden zones areas off limits
• airmen information notams
• ADS-radar free surveillance is a digital data link for automatic dependent surveillance (ADS-radar free surveillance) in the terminal controller area.
• the system preferably uses X;25 carrier sense multiple access (CSMA) digital communications using frequency division multiplexing (FDM). This technique uses the existing VHF aeronautical spectrum or other available RF spectrum.
• CSMA carrier sense multiple access
• FDM frequency division multiplexing
• the data radios used in the practical embodiment of the invention featured 25 kilohertz channel spacing versus the 50 kilohertz spacing still in use today. Recently the Federal Communication Commission (FCC) delayed the date when 25 KHz channel spacing will be required for all aviation users until 1997.
• the aeronautical VHF band operates at frequencies from 118 MHz to 136.975 MHz, giving a total of 760 channels based on 25 KHz channel spacing. Since spectrum is not infinite, sensible use is necessary.
• the following model is used to provide insight into possible system capacity and operational tradeoffs. The model uses data for the New York Metroplex and southern New Hampshire area.
• Traffic control area air and ground targets transmit position to tower air traffic controller.
• the data link is full duplex over two channels, to and from the aircraft and control tower air traffic control facility.
• Non-moving aircraft will report positions only once per minute or upon tower interrogation.
• Moving aircraft will broadcast position once per second on approach and departure otherwise every two seconds or upon interrogation.
• Radio frequency transmission rate is typically 4800 baud.
• Frequency agile (scanning) radios are used with 760 channels.
• Selected channels are dedicated to tower broadcasts (ATIS, interrogation, differential corrections, etc.).
• the ADS message handler automatically retransmits on another available channel.
• Each aircraft broadcasts its ADS message as defined above.
• the message consists of the following data:
• ATC system is based on ECEF positions, only maps are in surface coordinates.
• the asterisks identify optional fields for designating and determining vehicle attitude in 3-D digital map data base.
• FIG. 5 shows a block diagram of a radio-based data link system which embodies the principles of the present invention.
• each airplane tries to get a connection on a particular channel, using the X.25 protocol. If an airplane is unable to use that channel within a predefined period of time, the airplane tries another randomly selected channel (FDM) .
• FDM randomly selected channel
• Another feature of the system is use of carrier sense multiple access bi-directional data link for tower to aircraft communication.
• Another feature of the system is use of earth centered, earth fixed (ECEF) navigation on the airport surface, and in the terminal airspace.
• ECEF earth centered, earth fixed
• Another feature of the system is use of three GPS antennas to determine aircraft attitude. Attitude of aircraft is then used to draw the aircraft in the 3-D digital map with the proper attitude. Antennas are placed at three known positions on the aircraft. The GPS positions are then used as handles to draw the aircraft into the 3-D map.
• the data link supports three ECEF positions in the data message, so the airplane can be shown at the proper attitude in the 3-D airport map presentation. Therefore, this information is provided in the data link message.
• ADS automatic dependent surveillance
• the data transfer rate varies, depending on the data rate needed for the airplane's present activity. For example, an aircraft which is not moving or is not occupied would transmit once every 60 seconds, an aircraft which is taxiing would transmit every 2 seconds, and an aircraft which is on approach or departure would transmit every second. This maximizes available bandwidth of aeronautical spectrum because each airplane would transmit at a minimum rate which is required at that phase of its flight. Reporting rates may be easily modified as conditions warrant.
• Another feature of the system is the construction of a position keyed data base which maintains the last position an aircraft reported.
• the data base When a plane taxis to a parking location, the data base maintains the plane's position when and after the aircraft is turned off. When the plane is used again and starts to move, the data base is updated with new position data. In this manner, the data base will be self loading and will eventually contain all aircraft in the airport.
• This concept is extensible to airport surface vehicles such as fuel trucks and buses.
• Another feature of the system is the use of precise velocity and acceleration information, derivable from GNSS navigation and position information, as inputs into collision projection algorithms based on the earth centered, earth fixed reference.
• Another feature of the system is the use of a multi- windowed display showing different sections or views of the airport in each window.
• Another feature of the system is the ability to use map layers and zones of the map to segregate information into various air traffic controllers' stations.
• Another feature of the system is the use of a position keyed aircraft data base to automatically filter aircraft. This would be performed using GPS position, the ADS data link, and the ground computer data base.
• Another feature of the system is man-machine interface capability in which the controller defines a departure and/or approach trajectory (air and surface) using the data entry device and 3-D airport map, or calls up a previously defined trajectory.
• the path contains waypoints, notam data and forbidden zone information. The information is drawn into the map and then waypoints are passed to the aircraft as part of ATC clearance.
• the air traffic control system matches the present position and the next on-board waypoint with stored trajectory data in air traffic control computer. An alarm is sounded if a preset threshold or deviation is exceeded, meaning the aircraft is off course.
• FIGS. 6-10 Further disclosure: FIGS. 6-10.
• Figure 6 shows the appearance of the screen 14 when a trajectory path 24, waypoints 25 and monumented survey points 26 are imposed on the digital map.
• the trajectory path is shown for a taxiing maneuver, but, of course, the appearance would be somewhat similar for other taxi maneuvers as well as take off and landing trajectories.
• Figure 6 also shows the appearance of the screen 14 when a forbidden zone 27 is imposed on the digital map.
• FIG 7 shows the major hardware components of the airport terminal control system.
• a GNSS message is transmitted via the vehicle's radio equipment 29 through the communication interface 30 to the ATC computer 32.
• the signals may include differential corrections broadcast by a differential base station 31.
• the computer operator has access to a variety of data entry devices 33 including, but not limited to, a keyboard 35, mouse, spaceball or trackball 36 to control the presentation on the computer display screen 34.
• Figure 8 shows the major software components of the airport terminal control system.
• the GNSS signals broadcast by the vehicles 37 and the differential corrections determined by the differential GNSS software 39 are processed by the Real Time Communication Handler 38 and sent to the ATC Processor 40.
• the ATC Processor uses the GNSS data to perform the following processing functions listed under item 41: projections, coordinate conversions, zone detection, layer filter, view control, alarm control and display updates.
• the ATC Processor software 40 also receives inputs from the Controller Interface 43 software.
• the Controller Interface uses the data received by the controller's inputs 44 to compose ATC commands which are sent to the ATC Processor 40 for processing. Commands affecting the presentation on the computer display screen 34 are sent by either the ATC Processor 40 or Controller Interface 43 to the Graphical Control 42 software.
• Both the ATC Processor and Graphical Control 42 software use the Monumentation, NOTAMS, Trajectories, Aircraft/Vehicle, Airport Map, ATIS Interface and Airport Status data bases 45 to manipulate the presentation on the computer display screen 14.
• Figure 9 shows the major hardware components of the aircraft-vehicle system.
• the Aircraft Computer 52 receives GNSS data from the on-board GNSS receiver 51 and, optionally, from other vehicles 48 through its radio 49 and communications interface device 50. Messages are received from the ATC Tower 47 through the same communications path. Differential correction broadcasts are received through the radio equipment 49 and communication interface 50 to the GNSS receiver 51 where they are processed internally and then passed to the Aircraft Computer 52.
• the operator has access to the on-board data entry and display devices 53 including, but not limited to, a keypad 55, mouse and a display screen 54.
• Figure 10 shows the major software components of the aircraft-vehicle system.
• the GNSS signals broadcast by other vehicles 57 (optional), the differential correction broadcasts 58 and ATC messages 59 sent from the tower or remote station are processed by the Real Time Communication Handler 59 and sent to the Aircraft Processor 61.
• GNSS messages from the on-board GNSS receiver 60 are also received by the Aircraft Processor 61.
• the Aircraft Processor uses both the remote and on-board GNSS data to perform the following processing functions listed under item 62: projections, coordinate conversions, zone detection, layer filter, view control, alarm control and display updates.
• ATC commands are processed upon receipt from the Real Time Communication Handler 59.
• Display updates to the airline/vehicle screen 19 are passed from the Aircraft Processor 61 software to the Graphical Control 60 software.
• Both the Aircraft Processor 61 and Graphical Control 63 software use the Monumentation, NOTAMS, Trajectories, Aircraft/Vehicle, Airport Map, ATIS Interface and Airport Status data bases 64 to manipulate the presentation on the computer display screen 19.
• Figure 11 shows aircraft in 3-D airport map. Aircraft are 3-D scaled representations of real aircraft. Aircraft are drawn into the map from a data base of various aircraft types.

Landscapes

• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Aviation & Aerospace Engineering (AREA)
• Computer Networks & Wireless Communication (AREA)
• Traffic Control Systems (AREA)
• Position Fixing By Use Of Radio Waves (AREA)

Applications Claiming Priority (5)

Publications (2)

Family

ID=27081648

Family Applications (1)

Country Status (5)

Families Citing this family (158)

Citations (2)

Family Cites Families (22)

• 1991
  • 1991-10-09 EP EP91919752A patent/EP0592436A1/de not_active Withdrawn
  • 1991-10-09 CA CA002070840A patent/CA2070840A1/en not_active Abandoned
  • 1991-10-09 WO PCT/US1991/007575 patent/WO1992006442A1/en not_active Application Discontinuation
  • 1991-10-09 AU AU88779/91A patent/AU8877991A/en not_active Abandoned
• 1993
  • 1993-09-07 US US08/117,920 patent/US5548515A/en not_active Expired - Lifetime
• 1996
  • 1996-05-21 US US08/651,837 patent/US5740047A/en not_active Expired - Lifetime

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events